Monitoring seismic wave velocities in situ

Earthquake Information Bulletin (USGS)
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Beginning in the early 1960's, reports from the Soviet Union described travel-time anomalies of 5 to 20 percent preceding large earthquakes. In the early 970's, similar observations began to be reported outside the U.S.S.R. The most convincing were anomalously low values of the velocity ration, Vp/Vs, before four earthquakes of magnitudes 2.5 to 3.3 at Blue Mountain Lake, N.Y.; the anomalies were based on large amounts of high-quality data. In Japan, significant decreases were observed in the travel-time ratio, ts/tp, before two thrust-type earthquakes of magnitudes 6. and 5.3. Finally, there is the much discussed report of an anomaly before the magnitude 6.4 San Fernando, Calif., earthquake of 1971 and the implication that the change was caused principally by a decrease in the velocity of the primary (P) wave.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Monitoring seismic wave velocities in situ
Series title Earthquake Information Bulletin (USGS)
Volume 11
Issue 6
Year Published 1979
Language English
Publisher U.S Geological Survey
Description 7 p.
First page 214
Last page 220
Online Only (Y/N) N
Additional Online Files (Y/N) N